Method for increasing an entropy flow in a turbomachine

ABSTRACT

The invention relates to a method for increasing the efficiency of a turbomachine, wherein a fluid guided through the turbomachine transfers kinetic energy to the turbomachine. The object of the invention is to increase the efficiency of a turbomachine. This object is achieved in that the fluid or at least one fluid component of the fluid is compressible, and that the flow velocity of the fluid reduced in the turbomachine ( 1 ) during the transfer of kinetic energy is increased directly downstream of the turbomachine ( 1 ) by a force F B  generated by means of a force field and acting in the direction of flow, by converting potential energy of the fluid into kinetic energy of the fluid to such an extent that the pressure of the fluid, which is reduced in the turbomachine ( 1 ), is thereby increased again to at least 0.1 times the pressure of the fluid upstream of the turbomachine ( 1 ). (FIG.  2 )

The invention relates to a method for increasing the efficiency of aturbomachine, wherein a fluid guided through the turbomachine transferskinetic energy to the turbomachine.

Thermodynamic cycles are used in many different ways to convert energyin technology. In the most important processes for public energy supply,most of the energy used is still supplied by fossil fuels thataccumulated on Earth over millions of years through photosynthesis. Thisis increasingly becoming a problem as humanity's energy needs rise,since these energy resources cannot be replaced in the same quantity.Furthermore, the use of these forms of energy causes a highenvironmental burden. Therefore, these forms of energy must increasinglybe replaced by regenerative forms of energy. However, this is associatedwith a number of problems.

The two primary quasi-unlimited energy sources are nuclear fusion in theSun and nuclear fission inside Earth (geothermal energy). They drive allthe energy cycles on Earth. This energy can then also be usedsecondarily, e.g., as wind power, hydropower or geothermal energy. Theamounts of primary energy released annually are more than sufficient tomeet people's energy needs. However, they are not available in everylocation and at every time. Furthermore, the development of renewableenergy sources often involves high costs. The long energy-payback timeand low yield factor are among the reasons for the continued large-scaleuse of fossil fuels.

Processes for energy conversion and storage and their efficienciestherefore play a decisive role. Up to now, only chemical energy (inmethane or hydrogen, for example) has been suitable for storing largeamounts of energy over longer periods of time (>6 months). Althoughbattery storage systems have good efficiencies, they are only analternative for mobile devices or daily storage because of the highcosts and rare materials required. Pumped-storage power plants can onlybe used in areas with large differences in altitude. Thermal energystorage, although theoretically offering a high energy-storage capacityper unit volume, requires large temperature differences to convert thisenergy into other forms of energy. This also increases thermal losses,however. Thermal storage units are therefore suitable for balancingdaily fluctuations in heat supply. They are of little significance forconversion into other forms of energy, as the efficiency of energyconversion is low.

Industrial energy supplies mainly use thermodynamic processes, where theoptimisation potential of gas or steam power plants is limited. Themaximum efficiency is limited by the maximum temperature achievable withthe material and the ambient temperature. The problems associated withenergy conversion using thermodynamic processes are particularly evidentin the case of the compressed-air-storage power plant, which has not yetachieved any commercial significance. When the air is compressed, thethermal energy is increased.

Since the underground storage tanks used cannot be thermally insulated,some heat energy is lost to the environment. When energy is released,the compressed air expands again, causing severe cooling and icing.Here, the energy lost during compression has to be replaced by burningnatural gas, for example. Since expansion is always required for thedelivery of pressure-volume work, a large temperature difference isaimed for in all thermodynamic processes.

In thermodynamic processes, a distinction is made between right-hand(delivery of pressure-volume work, heat engines) or left-hand(refrigerating machines, heat pumps) processes.

In essence, thermal energy is the sum of the effects of various forms ofkinetic energy. The (internal) energy of a thermodynamic microstateconsists of three essential components: translational energy E_(trans),vibrational energy E_(vib) and rotational energy E_(rot). Thus, eachform of energy can also be assigned a corresponding share of the totalentropy (S_(ges)=S_(vib)+S_(rot)+S_(trans)).

E_(vib) is relatively low for gases and can usually be neglected. Formonatomic gases, E_(trans) dominates. In the liquid state, E_(trans)=0and E_(rot) becomes dominant. In the solid state, molecular rotation isalso not possible and the total energy is determined by E_(vib). Inpolyatomic gases and at interfaces between gases, liquids and solids,these different forms of kinetic energy interact. This establishes adynamic equilibrium between kinetic forms of energy.

Only the translational part (E_(trans)) of the internal energy can beused directly to perform pressure-volume work. However, if thetranslational momentum (p_(trans)) decreases, the vibrational androtational energy and entropy are transferred to the translationalmovement. The translational energy and entropy increase again and thevibrational and rotational components decrease. The momentum determinesthe direction of the thermal energy flow and correlates withtemperature. In right-hand thermodynamic processes, thermal energy issupplied and mechanical energy is released when the translationalmomentum of the molecules is high (high temperature). At low momentum(low temperature), thermal energy is dissipated and mechanical energy issupplied. Because of the energy-momentum relationship, more mechanicalenergy is released than supplied. With a heat pump (left-hand system),the process is inverted. This means that mechanical work must be addedto the overall process. The ratio of the momentum intensity thus alsodetermines the efficiency.

The conversion of thermal energy into directed mechanical energy cantake place with an isentropic change of state. However, the operatingprinciples of a piston machine and a turbomachine are different. Theforce acting on a piston results from the mean momentum of the moleculesand the frequency of impacts (pressure). The molecules hit the pistonwith a mean velocity approximately equal to the speed of sound. The meanmomentum is thus calculated from the molecular mass and the speed ofsound (p=m*v_(s)). If the piston moves during an expansion, the relativespeed drops below the speed of sound. This means that the mean effectivemomentum is always slightly below the momentum at the speed of sound.With compression, on the other hand, it is slightly higher than themomentum at the speed of sound, since the piston is moving in theopposite direction.

Turbomachines are known from the prior art. In these, a compressibleworking medium is first accelerated by a convergent nozzle. Unlike manyother forms of energy, thermal energy has no effective direction vectorin space. It acts in all spatial directions simultaneously. Theconvergent nozzle converts this undirected translational energy intodirected lateral energy of the flow. However, this means that the flowcan only be accelerated up to the speed of sound, since above this speedthere is no translational energy available for the conversion. A deLaval nozzle offers a solution for acceleration beyond the speed ofsound. With this, after reaching the speed of sound, the flow crosssection is enlarged again. The pressure-volume work so released permitsfurther lateral acceleration. One disadvantage is the reduction inentropy due to the increase in cross section of the de Laval nozzle. Onealternative is described in DE 10 2014 004 237 A1. Here, a mixture ofgas and a liquid is mixed and accelerated. By adding rotational andvibrational energy from the fluid, the multiphase flow can beaccelerated beyond its speed of sound without increasing the crosssection. According to the energy equation E=m/2*v², the higher speedenables a higher amount of energy to be delivered and thus provides ahigher efficiency compared to a piston machine. A similar process isdescribed in DE 10 2012 108 222 A1. Here, too, a multiphase flow(air/water) is accelerated to a supersonic speed. The water componenthere increases the mass of the flow and compensates for the reduction intranslational energy by supplying the rotational and vibrational energyof the water molecules.

A little-considered problem with turbomachinery is the acceleration ofthe molecules downstream of the turbomachinery. Please refer to FIG. 1 .The molecules move with velocity v₁ in the flow channel (see FIG. 1 ).On hitting the turbomachine (4), they deliver a large part of theirlateral kinetic energy to the turbomachine and move on with velocity v₂.Since velocity v₂ is very low due to the energy dissipated, the speed ofsound (v_(s)) dominates in the molecular movement. Thus, a force F₂ alsoacts against the direction of flow. This force is influenced by theintensity and frequency of molecular impacts against the direction offlow and limits the efficiency of the turbomachine.

In order to reduce the force and increase the efficiency, thermal energyis dissipated to an external reservoir in the technique. This lowers thetemperature and thus the intensity of the molecular impulses. However,in order to significantly reduce the intensity, a great deal of thermalenergy and entropy must be dissipated. In the (Clausius-)Rankine andorganic Rankine cycles, the translational velocity is reduced to zero bycondensation. However, the entire translational energy must bedissipated, as must part of the vibrational and rotational energy in thecase of polyatomic molecules.

DE 26 54 097 A1 describes the operation of a right-hand cycle belowambient temperature. This has the problem of dissipating the thermalenergy into the environment, however. The author proposes a heat pump asa solution, but does not explain why this heat pump should require lessdrive energy than is additionally released by the greater temperaturedifference in the right-hand process. Thermal and frictional losses atthe heat pump mean additional thermal energy must be dissipated, which,according to the law of conservation of energy, reduces the usefulenergy of the overall system.

DE 10 2017 127 716 A1 describes a method for cooling by isothermalcompression. The method uses the force of gravity for isothermalcompression. The turbomachine is not located in the flow channel of themultiphase flow, however, and the aim of the method is compressionupstream of the turbomachine. Because of the low entropy flow in theturbomachine in relation to the multiphase flow, the process is notintended for the generation of mechanical energy, but for cooling.

The object of the invention is to increase the efficiency of aturbomachine.

According to the invention, this object is achieved with a method havingthe characteristics of Claim 1. The object is further achieved with amethod according to Claim 2. Advantageous embodiments of the methodsaccording to Claims 1 and 2 are presented in Claims 3 to 9.

In the method according to the invention, a flow of a compressible fluidis fed to a turbomachine. In the turbomachine, kinetic energy istransferred from the fluid to the turbomachine. After a polytropicexpansion in the turbomachine, the flow velocity of the fluid downstreamof the turbomachine, which is reduced in the turbomachine during thetransfer of kinetic energy, is increased by a force F_(B), generated bya force field and acting in the direction of flow, by convertingpotential energy of the fluid into kinetic energy of the fluid to suchan extent that the pressure of the fluid, which is reduced in theturbomachine, is thereby increased again to at least 0.1 times thepressure of the fluid upstream of the turbomachine. Technically, ofcourse, the increase in pressure of the fluid downstream of theturbomachine is limited to the pressure of the fluid upstream of theturbomachine. The force F_(B) in the direction of flow is generated by aforce field, such as a gravitational field, a centrifugal field, amagnetic field or an electric field. The dislocation of the molecules inthe direction of flow causes potential energy due to the field to beconverted into kinetic energy.

In the method according to Claim 1, the force F_(B) acting in thedirection of flow partially or completely compensates for athermodynamic force F₂ acting against the direction of flow. Theincrease in the flow velocity of the fluid downstream of theturbomachine due to the force F_(B) causes an increase in the pressureof the fluid in the further course of the flow downstream of theturbomachine. The resulting reduction in the pressure of the fluiddirectly downstream of the turbomachine increases the efficiency of thepolytropic expansion in the turbomachine. The molecules of the fluid areaccelerated to a velocity v₂ by the force F_(B). If the fluid is a gas,for example, the velocity v₂ should be at least 0.3 times the speed ofsound in the fluid. F_(B) is thus of the same order of magnitude as F₂.For a mixture of two gases, the velocity v₂ should be at least 0.3 timesthe weighted average of the speeds of sound in the two gases. Theacceleration of the molecules of the fluid downstream of theturbomachine has a great influence on its efficiency. The aim of theacceleration is to reduce the pressure and thus the force against thedirection of flow directly downstream of the turbomachine. The greaterthe acceleration downstream of the turbomachine, the greater theinfluence of the method according to the invention on the efficiency ofthe turbomachine, although the increase in the flow velocity downstreamof the turbomachine is of course limited to the flow velocity upstreamof the turbomachine. Compared to a flow velocity of 0.3 times the speedof sound in the fluid, higher efficiencies are achieved for theefficiency of the turbomachine if the flow velocity downstream of theturbomachine is accelerated, for example, to 0.5 times or 0.6 times or0.8 times the speed of sound in the fluid, or to the speed of sound inthe fluid, whereby the flow velocity upstream of the turbomachine isthen at least about 0.51 times or 0.61 times or 0.81 times or 1.01 timesthe speed of sound in the fluid.

If, on the other hand, the fluid consists of a gas and a liquid, thevelocity v₂ should be so high that the translational velocity of themolecules of the gas (the compressible fluid component) is at least 0.3times the speed of sound in the gas.

In methods according to the prior art, acceleration of the flow isachieved by dissipating thermal energy and entropy to the environment.In the method according to the invention, the dissipation of thermalenergy necessary for acceleration is eliminated or at leastsignificantly reduced by generating the acceleration of the molecules ofthe fluid with the force F_(B) acting through a force field in thedirection of flow. The force F_(B) is independent of the molecule'sstate of motion and can thus accelerate even molecules with high kineticenergy. A higher kinetic energy and the associated higher kineticmomentum of the molecules makes it possible to dissipate thermal energyto an external reservoir (energy sink) with greater intensity(temperature) after acceleration.

According to Claims 3 and 4, the compressible fluid is accelerated inthe direction of flow upstream of the turbomachine with a convergentnozzle. A divergent nozzle and/or a compressor are located downstream ofthe turbomachine in the direction of flow.

The compressible fluid is thus first accelerated at the convergentnozzle, whereby translational kinetic energy of the molecules(E_(trans)) is converted into lateral kinetic energy (E_(lat)), thevibrational and rotational energies (E_(vib), E_(rot)) of the moleculesof the fluid are converted into translational energy (E_(trans)) and thefluid flow is accelerated to a velocity v₁. This also increases thetranslational entropy component (S_(trans)). Energy and momentum arereleased in the turbomachine so that the velocity of the fluid flow issignificantly reduced again. The force F_(B) in the flow channel thenaccelerates the molecules of the fluid downstream of the turbomachine tovelocity v₂. In the divergent nozzle and/or compressor, the energy andentropy components at constant pressure (E_(trans), S_(trans)) thendecrease through conversion into vibrational and rotational energy.These components do not have to be dissipated externally. A completecompensation of F₂ would require the acceleration of the molecules tothe speed of sound. A significant increase in the efficiency of theturbomachine is achieved for a velocity v₂ with 0.3 or more times thespeed of sound in the fluid. When accelerated to the speed of sounditself, a vacuum is created directly downstream of the turbomachine. Inthe divergent nozzle, part of the lateral kinetic energy is convertedback into undirected thermodynamic motion, whereupon the temperature andpressure increase. This means that less or no thermal energy has to bedissipated into the environment, which reduces global warming due tothermodynamic processes. The flow then moves on with a low lateralvelocity (v₃).

The lateral velocity (v₁) of the molecules upstream of the turbomachineshould be greater than the speed of sound. At a higher speed, accordingto E=m/2*v², more energy is released than is needed to accelerate themolecules to the speed of sound with F_(B). Fundamentally, accelerationabove the speed of sound is based on the principle of relativity. In theconvergent nozzle, the translational movement of the molecules isconverted into a lateral movement in the direction of flow. However, themean velocity relative to an observer outside the flow remains constant.This means that no additional energy can be supplied from outsidedespite the lower temperature. However, with respect to the vibrationaland rotational energy carried in the flow, the intensity of thetranslational motion of the molecules decreases. This results in aconversion of vibrational and rotational energy into translationalenergy, which can thus be used in addition to the lateral acceleration.The lateral velocity can thus be higher than the mean translationalvelocity (speed of sound) at the entrance of the convergent nozzle. Inthis way, energy with lower intensity (momentum, temperature) can besupplied. This increases the energy conversion and energy efficiency ofthe process.

With negative acceleration in the divergent nozzle, the energy flow actsin the opposite direction. The lateral kinetic energy is converted intoa disordered translational movement of the molecules and increases itsintensity. This means that part of the translational energy can beconverted into vibrational and rotational energy. If thermal energy isdissipated to the environment, the vibrational and rotational energymust also be dissipated. However, if the flow is additionallyaccelerated beforehand by the external force F_(B), the proportion ofvolume-independent vibrational and rotational energy increases. Moreenergy can therefore be stored in the flow and released again during arenewed acceleration.

The ratio of vibrational and rotational energy to translational energyis described by the isentropic coefficient. Therefore, the fluid in theworking temperature range should have at least one fluid component withan isentropic coefficient of less than or equal to 1.4. A higherefficiency is achieved with a fluid where at least one fluid componenthas an isentropic coefficient less than or equal to 1.2. The efficiencyis even higher with an isentropic coefficient less than or equal to 1.1.

The fluid can be a gas or a multiphase flow, whereby, for the purposesof the application, “multiphase flow” is understood to mean both gaseousmixtures and mixtures of gases and liquids. In a multiphase flow,substances with high isentropic coefficients (c_(p)/c_(V)), such ashelium, should be mixed with substances with low isentropiccoefficients, such as n-butane. The non-volume-dependent component ofthermal energy (vibrational and rotational energy) should have a highheat capacity in relation to the translational energy. In principle, itis also possible to calculate an isentropic coefficient (c_(p)/c_(V))for fluids. This has a value around 1. The advantage of gas mixtures isthe better energy exchange due to the larger effective area of theindividual molecules. In pure substances (fluids consisting of one gas),the proportion of vibrational and rotational energy is determined by themolecular structure. Gases with a very low isentropic coefficient andhigh molecular mass should therefore be used. A multiphase flowconsisting of a gaseous and a liquid fluid component can also be used,whereby, in order to generate the pressure reduction downstream of theturbomachine, the velocity v₂ should be so high that the translationalvelocity of the molecules of the gas (compressible fluid component) isat least 0.3 times the speed of sound in the gas.

In the further development of the method according to Claim 6, a fluidmixture is used as the working medium. This combines a fluid with highvapour pressure and a fluid with low vapour pressure. The pressure atthe inlet of the convergent nozzle is selected such that both fluids areliquid (vibrational and rotational energy). If the pressure drops duringacceleration in the convergent nozzle, the fluid with the higher vapourpressure reaches its boiling point. By transferring vibrational androtational energy from the fluid with the low vapour pressure, the fluidwith the high vapour pressure is completely vaporised. The physicaleffect of evaporation described is also the basis of cavitation, whichis usually to be avoided in turbomachinery. In the method according tothe invention, however, this effect is deliberately intensified in orderto achieve a high acceleration of the flow. The now compressible fluid(with translational energy) is strongly accelerated in the flow channeldue to the increase in volume and gives off energy and momentum to theturbomachine. By increasing the pressure in the divergent nozzle and/orcompressor, the condensation point is reached and the compressiblecomponent of the fluid gives up its translational energy to theincompressible fluid component (vibrational and rotational energy).

In an alternative further development according to Claim 7, a reversiblechemical process can also be used. In this process, a gas dissolved in aliquid is fed to the convergent nozzle. If the pressure drops duringacceleration in the convergent nozzle, the reaction equilibrium changesand gas escapes from the solution. This provides translational energyfor high acceleration. The compressible fluid gives off energy andmomentum to the turbomachine. By increasing the pressure in thedivergent nozzle and/or compressor, the reaction equilibrium changesagain and the gas dissolves in the liquid due to the chemical reaction.Translational energy is converted into vibrational and rotationalenergy.

The externally supplied energy for F_(B) can be supplied by, forexample, a gravitational force, a magnetic force, an electrical force ora centrifugal force. Likewise, a mechanical force can also be providedby a further turbomachine operated with energy supplied from outside,whereby this turbomachine is then arranged downstream of the divergentnozzle in the direction of flow.

Table 1 shows a comparison of the acceleration times and distances dueto the gravitational force on Earth (˜9.81 m/s²) in free fall from zeroto the speed of sound (v_(s)) for various substances at normal pressureand temperature (1 bar; 300K).

TABLE 1 Substance v_(s) (m/s) t (s) s (m) Helium 1020 104 53028 Nitrogen353 36 6351 Carbon dioxide 269 27 3688 Xenon 174 18 1543 Water/airmixture 10 1 10

The table shows that the gravitational force is particularly suitablefor media with very heavy molecules and for multiphase flows. Sinceacceleration of the fluid to at least 0.3 times the speed of sound inthe divergent nozzle increases the pressure and temperature, the processcan also be operated below ambient temperature. Lower temperatures alsomake shorter acceleration distances and acceleration times possible dueto the lower speed of sound. In a mixture of water and air with a highmass fraction of water, the water pressure increases from 0 bar to 1 barover a fall of 10 m. This means that the air molecules are alsocompressed to this pressure and thus move at the speed of sound in air.The speed of sound in the overall flow, on the other hand, is muchlower. A fall of just 10 m is thus sufficient for generating a vacuumdownstream of the working machine. In a gravitational divergent nozzle,the speed of the molecules in or upstream of the divergent nozzle cantherefore be increased. This reduces the lower pressure in theisentropic expansion and increases the efficiency of the thermodynamicprocess.

Greater forces than that of gravity can be generated with a centrifugalforce. This shortens the acceleration distances and thus the dimensionsof the thermodynamic machine. For this purpose, the thermodynamicmachine is designed to be rotationally symmetrical and rotates about itsrotational axis. The rotation creates an inhomogeneous phase space. Theexpected value (ensemble mean) increases with the distance from therotational axis, as thus do the pressure, temperature and density. Ifthe tangential velocity approaches the speed of sound, a near vacuum isformed at the rotational axis. The compressor serves to compensate forprocess losses (such as friction) and does not have to perform a greatdeal of pressure-volume work. It pushes the working medium into theconvergent nozzle, where it is accelerated. An additional accelerationoccurs due to the thermodynamic force with the centrifugal force F_(Z)decreasing in the direction of flow. In the turbomachine, kinetic energyis extracted from the molecules at high speed. Afterwards, the moleculesin the flow channel are accelerated in the direction of flow by F_(Z).In the divergent nozzle, the pressure and the temperature increase.Upstream of the compressor, thermal energy (Q₂) can optionally bedissipated using a heat exchanger. Thermal energy (Q₁) is fed indownstream of the compressor. This reduces the pressure-volume work onthe compressor. The transport of thermal energy via the wall of the flowchannel is possible by thermal conduction but also by a fluid in aparallel flow channel.

A thermodynamic machine with a centrifugal convergent nozzle and acentrifugal divergent nozzle makes it possible to accelerate themolecules laterally beyond their speed of sound by changing thecentrifugal force. Homogeneous substances and also multiphase flows canbe used. When using multiphase flows with different isentropiccoefficients, the temperature change is reduced and the tangentialvelocity and thus the radius can be reduced due to a greaterincompressible component (rotational and vibrational energy). Thetranslational component of the entropy flow increases duringacceleration and thus also leads to a higher lateral velocity in theturbomachine.

Depending on the application, the turbomachine can be a turbine or anMHD generator.

In principle, however, the method according to the invention is suitablefor increasing the efficiency of any polytropic expansion. For expansionin a piston machine, the energy is extracted at the speed of sound andthe acceleration energy is supplied in the flow channel at relativespeeds below the speed of sound. In the case of turbomachinery, however,a greater effect can be expected due to the higher achievable relativevelocity during the delivery of mechanical energy. In piston machines,because of the discontinuous mode of operation, several pistons mustalso be operated in parallel and with offset phases so that a continuousflow is created in the flow channel.

Exemplary embodiments of the invention are described below withreference to the drawings.

THE DRAWINGS SHOW

FIG. 1 A flow of fluid with a turbomachine according to the prior art

FIG. 2 An arrangement for using the method according to the invention

FIG. 3 A further arrangement for using the method according to theinvention

FIG. 4 A thermodynamic cycle with a centrifugal convergent nozzle and acentrifugal divergent nozzle

FIG. 5 A gravitational divergent nozzle

FIG. 6 A thermodynamic cycle with an MHD generator

FIG. 7 A heat pump with branched entropy circuit

FIG. 8 A heat pump with open branched entropy circuit

FIG. 9 A heat engine with branched entropy circuit

FIG. 10 A hydropower machine

FIG. 1 shows a flow of a fluid with a turbomachine 1 according to theprior art. Turbomachine 1 is shown as an impeller. The fluid flowtransfers part of its kinetic energy to the turbomachine 1, where it isdissipated as work. The molecules M of the fluid move with the velocityv₁ in the flow channel and give off a part of their lateral kineticenergy to the turbomachine at its impellers and then move on with thevelocity v₂.

FIG. 2 shows an arrangement for using the method according to theinvention to increase an entropy flow in a turbomachine 1. For thispurpose, a compressible fluid is polytropically expanded in turbomachine1, which has the form of a turbine. After the polytropic expansion, anadditional force F_(B) acts on the molecules M of the fluid in thedirection of flow, so that the molecules M are accelerated in thedirection of flow by this force. The force F_(B) acting in the directionof flow is generated by a force field, whereby the fluid's potentialenergy is converted into kinetic energy of the fluid. This force F_(B)accelerates the molecules M of a fluid consisting of gas or a gasmixture downstream of the turbomachine to at least 0.3 times the speedof sound in the fluid, so that the pressure of the fluid, reduced in theturbomachine, is increased again to at least 0.1 times the pressure ofthe fluid upstream of the turbomachine and thus the pressure reductionnecessary for increasing the efficiency of the turbomachine is achieveddirectly downstream of the turbomachine. In the embodiment shown, theforce F_(B) can be the gravitational force, for example. In the case ofa fluid consisting of a mixture of gas and liquid, the pressurereduction is achieved directly downstream of the turbomachine when thevelocity v₂ of the fluid is at least so high that the translationalvelocity of the molecules M of the gas (compressible fluid component) isat least 0.3 times the speed of sound in the gas.

FIG. 3 shows a further arrangement for using the method according to theinvention. The polytropic expansion in the turbomachine 1 is preceded bya convergent nozzle 2, so that the compressible fluid is acceleratedbefore the turbomachine 1. A divergent nozzle 3 is located downstream ofthe turbomachine 1 in the direction of flow. Depending on the desiredincrease in efficiency for the turbomachine, the acceleration at theconvergent nozzle upstream of the turbomachine can, for example, be upto 0.31 times or 0.51 times or 0.61 times or 0.81 times or 1.01 timesthe speed of sound in the fluid. Downstream of the turbomachine, thefluid is then accelerated again as close as possible to the value of theflow velocity upstream of the turbomachine (0.3 times or 0.5 times or0.6 times or 0.8 times or equal to the speed of sound in the fluid). Acompressor 5 is connected downstream of the divergent nozzle 3, althoughthis is optional here. In another embodiment not shown, the compressor 5is provided instead of the divergent nozzle 3. The fluid can be a puresubstance (a gas), a mixture of gases or a mixture of gas and liquid andthe force F_(B) can be the force due to gravity, for example.

FIG. 4 a and FIG. 4 b show two arrangements for using the methodaccording to the invention in a thermodynamic cycle with a centrifugalconvergent nozzle and a centrifugal divergent nozzle. A flow channelwith a fluid is set in rotation around a rotational axis 4. This causesa centrifugal force F_(Z) to act on the fluid and causes the density ofthe fluid to increase with distance from the rotational axis 4. Acompressor 5 is placed at the location with the highest rotationalspeed. The turbomachine 1 is arranged on the rotational axis 4. Thefluid is first accelerated in the convergent nozzle 2 and gives offenergy and momentum to the turbomachine 1. Downstream of theturbomachine 1, the fluid is accelerated by the increasing centrifugalforce, and the pressure in the divergent nozzle 3 is increased again.Here, too, the molecules M of the fluid are accelerated to at least 0.3times the speed of sound in the fluid. An amount of thermal energy Q₁can be fed in between the compressor 5 and the convergent nozzle 2.Optionally, an amount of thermal energy Q₂ can be dissipated between thedivergent nozzle 3 and the compressor 2. In the embodiment according toFIG. 4 a , the turbomachine 1 is arranged radially to the rotationalaxis. In FIG. 4 b , the turbomachine 1 is arranged axially to therotational axis in an alternative embodiment. Again, the fluid can be apure substance (a gas), a mixture of gases or a mixture of gas andliquid. In the case of a fluid consisting of gas or mixture of gases,the fluid is also accelerated here downstream of the turbomachine to atleast 0.3 times the speed of sound in the fluid, so that the pressure ofthe fluid, reduced in the turbomachine, is increased again to at least0.1 times the pressure of the fluid upstream of the turbomachine andthus the pressure reduction necessary for increasing the efficiency ofthe turbomachine is achieved directly downstream of the turbomachine. Inthe case of a fluid consisting of a mixture of gas and liquid, thepressure reduction is achieved directly downstream of the turbomachinewhen the velocity v₂ of the fluid is at least so high that thetranslational velocity of the molecules M of the gas (compressible fluidcomponent) is at least 0.3 times the speed of sound in the gas.

In the embodiment shown, the force F_(B) is therefore provided by thecentrifugal force F_(Z). The thermodynamic machine described with acentrifugal convergent nozzle and centrifugal divergent nozzle is thusalso suitable for use in places with low gravity (such as in space).

In one embodiment, the arrangements according to FIG. 3 or FIG. 4 a /4 buse a multiphase flow in which a phase change (evaporation/condensation)of a component or a reversible chemical reaction is used. If, forexample, a mixture of water and isobutane is fed into the convergentnozzle 2 at 4 bar and 300 K, both components are liquid. Due to theacceleration in the convergent nozzle 2, the pressure drops and theisobutane reaches its boiling point. By adding rotational andvibrational energy (of the molecules M) from the liquid water, it canevaporate. The increase in volume further accelerates the flow. Part ofthe kinetic energy is released in the turbomachine 1. The flow is thenlaterally accelerated by the gravitational or centrifugal force. Due tothe increased pressure in the divergent nozzle 3 and/or in the followingcompressor 5, the gas condenses with a major reduction in volume.However, the energy released in the process does not have to bedissipated externally, but is stored in the circuit in the form ofvolume-independent vibrational and rotational energy.

When using a water-carbon-dioxide mixture, the carbon dioxide dissolvesin the water and reacts to form carbonic acid. When the pressure dropsin convergent nozzle 2, the equilibrium of the solution decreases andgaseous carbon dioxide is released in the flow channel, accelerating theflow. Since a concentration equilibrium is established in the solution,an even release of gas is to be expected here. After the releasingenergy in the turbomachine and accelerating in the flow channel, the gasgoes back into solution due to the pressure increase in the divergentnozzle 3 and/or in the following compressor 5 and reduces the volume ofthe multiphase flow. Carbon dioxide then reacts with the water to formcarbonic acid.

The choice of components has a significant influence on the workingpressure. For substances with low vapour pressures (e.g., anisopropanol/water mixture), the pressure upstream of the convergentnozzle 2 may be less than 1 bar. This simplifies the design. Due to thehigh density of liquid water, the energy density and entropy flow arenevertheless very high. This makes it possible to achieve a very highspeed and energy output in the turbomachine with compact dimensions.

FIG. 5 shows a gravitational divergent nozzle as a further arrangementfor using the method according to the invention. A fluid is acceleratedin the convergent nozzle 2 and fed to the turbomachine 1. The flowchannel and divergent nozzle 3 are arranged in the direction of gravity,whereby the gravitational force F_(G) acts as a force F_(B) andaccelerates the molecules M of the fluid by converting potential energyinto kinetic energy. The machine is dimensioned such that the volumebetween the compressor 5 and the convergent nozzle 2 is greater than thevolume between the turbomachine 1 and the compressor 5. Alternatively, apressure-balancing vessel 6 can be fitted. In this way, the compressor 5creates a negative pressure in the turbomachine 1, which increases theefficiency. An amount of thermal energy Q₁ is fed in between thecompressor 5 and the convergent nozzle 2. Optionally, an amount ofthermal energy Q₂ can be dissipated between the divergent nozzle 3 andthe compressor 5.

Since only the relative speed of the flow is relevant for the energysupply in turbomachines 1, energy can be extracted in a narrow flowchannel at high speed with a turbomachine 1 and fed in within a widerflow channel at low speed. According to E=m/2*v², more energy isreleased at high speed than is fed in at low speed. The mechanical force(F_(m)) supplied by the compressor 5 acts like the gravitational forceF_(g) and reduces the pressure downstream of the turbomachine 1. Forthis purpose, the pressure-balancing vessel 6, which keeps the pressureat the inlet of the convergent nozzle 2 constant, is installed betweenthe compressor 5 and the convergent nozzle 2. For compressible fluids,pressure balancing can also be achieved by having a large volumeupstream of the convergent nozzle 2 compared to the volume betweendivergent nozzle 3 and the compressor 5. In open processes, thesurrounding atmosphere can be used for pressure balancing. If mechanicalwork is supplied to the compressor 5, the pressure at the outlet of thedivergent nozzle 3 drops. This allows the pressure at the outlet of theturbomachine 1 to drop to almost zero, which permits high flowvelocities and thus high efficiency. For this, sufficient energy must beavailable for the acceleration in the convergent nozzle 2, and this canbe provided by a high proportion of vibrational and rotational energy(in the case of complex molecules M or multiphase flows). Thisaccelerates the fluid to supersonic speeds even without a de Lavalnozzle. Since the thermal energy Q₁ does not need to be fed in at a hightemperature, but is only transferred when the relative translationalvelocity of the molecules M within the flow is reduced, thevolume-effective heat capacity and thus the entropy flow I_(S) at theworking machine 1 increases. According to P=T*I_(S) (P=power,T=temperature, I_(S)=entropy flow), the power P increases at constantinput temperature.

The compressor 5 should be located near the lowest point in the cycle.The energy W₂ required to operate the compressor 5 can be suppliedpartly or completely by the mechanical energy W₁ released in theturbomachine 1.

The fluid used in the arrangement according to FIG. 5 can be a puresubstance (a gas), a gas mixture or a mixture of gas and liquid. In thecase of a fluid consisting of gas or mixture of gases, the fluid is alsoaccelerated here downstream of the turbomachine to at least 0.3 timesthe speed of sound in the fluid, so that the pressure of the fluid,reduced in the turbomachine, is increased again to at least 0.1 timesthe pressure of the fluid upstream of the turbomachine and thus thepressure reduction necessary for increasing the efficiency of theturbomachine is achieved directly downstream of the turbomachine. In thecase of a fluid consisting of a mixture of gas and liquid, the pressurereduction is achieved directly downstream of the turbomachine when thevelocity v₂ of the fluid is at least so high that the translationalvelocity of the molecules M of the gas (compressible fluid component) isat least 0.3 times the speed of sound in the gas.

FIG. 6 shows a thermodynamic cycle with a turbomachine designed as anMHD generator as a further arrangement for using the method according tothe invention. A mixture of an electrolyte (e.g., an ionised solution)and a compressible fluid is used as the working medium. The mixture isaccelerated in the convergent nozzle 2 and flows through a magneticfield of the turbomachine 1, which is designed as an MHD generator. Inthe process, the charge carriers of the electrolyte are deflected to theleft or right and the electrical energy is dissipated via theelectrodes. In the divergent nozzle 3, the flow velocity is reduced,converting translational energy into vibrational and rotational energy.

The fluid is compressed in the compressor 5 and flows back to theconvergent nozzle 2. The volume between the compressor 5 and theconvergent nozzle 2 must be larger than the volume between the MHDgenerator and the compressor 5. Alternatively, a pressure-balancingvessel 6 can be fitted. In this way, the compressor 5 creates a negativepressure downstream of the MHD generator, which accelerates the flow andincreases the efficiency. The thermal energy Q₁ is fed in upstream ofthe convergent nozzle 2. Optionally, thermal energy Q₂ can be dissipateddownstream of the divergent nozzle 3.

One advantage of this arrangement is a higher achievable magnetic fieldstrength in the narrow flow channel compared to the wider flow channelof a de Laval nozzle. Furthermore, the charge-carrier density in theelectrolyte is high, which permits compact dimensions of the machine. Incontrast to when an ionised gas is used, the process can also take placeat ambient temperature, which reduces the demands on materials and thecosts.

FIG. 7 shows a heat pump with a branched entropy circuit for theapplication of the method according to the invention. A fluid consistingof a first fluid component and a second fluid component, wherein atleast the second fluid component is compressible, is accelerated in aconvergent nozzle 2 and fed to a turbomachine 1. Downstream of theturbomachine 1, the fluid can optionally be accelerated by the forceF_(B) in the flow channel and divergent nozzle 3, which reduces thepressure at the outlet of the turbomachine 1. Afterwards, the secondfluid component, which has a larger c_(p)/c_(V) ratio compared to thefirst fluid component, is separated in the separator 7 and fed to thecompressor 5.2, where the second fluid component is accelerated and/orcompressed. The temperature increases due to the compression. The firstfluid component is fed to the compressor 5.1, wherein the temperaturedoes not change or changes only very slightly compared to the secondfluid component. This allows thermal energy Q₁ to be fed into the firstfluid component by means of the heat exchanger 8.1. The second fluidcomponent, compressed in compressor 5.2, releases its thermal energy Q₂by means of the heat exchanger 8.2. Afterwards, both fluid componentsare combined in the mixer 9. The volume between the turbomachine 1 andthe compressor 5.2 must be smaller than the volume between thecompressor 5.1 and the mixer 9. Alternatively, a pressure-balancingvessel 6 can be fitted. In this way the compressors 5.1 and 5.2 generatea negative pressure in the separator 9, which increases the efficiencyof the turbomachine 1. For a significant difference, within the workingtemperature range at compressors 5.1, 5.2, the ratio c_(p)/c_(V) of thesecond fluid component should be at least 1.1 times the ratioc_(p)/c_(V) of the first fluid component.

The dimensioning of the entropy flows has a great influence on theefficiency. With the same thermal power at the inlet and outlet (P₁=P₂),it follows from I_(S1)>I_(S2) that, according toP₁=T₁·I_(S1)=T₂·I_(S2)=P₂, also T₂>T₁. This means that the mechanicalenergy supplied−W_(mech)=|W₄|+|W₅|−|W₃|—only has to compensate for theprocess losses. With T₂=T₁=T and I_(S1)>I_(S2), it follows that P₁>P₂. Astream of energy then flows out of the machine:P=T₂·I_(S2)−T₁·I_(S1)=T·(I_(S2)−I_(S1)). This means that, depending onthe dimensioning of the entropy flows, the machine can also work as aheat engine.

The mass flows of the fluid components should be dimensioned such thatan entropy flow I_(S1) of the first fluid component at the compressor5.1 is greater than an entropy flow I_(S2) of the second fluid componentat the compressor 5.2. For a significant increase in efficiency, themass flow for I_(S1) at the compressor 5.1 should be at least five timesgreater than the mass flow for I_(S2) at the second compressor 5.2. Theentropy flow at the inlet of the turbomachine is equal to the sum of thetwo entropy flows I_(S1) and I_(S2).

FIG. 8 shows a heat pump with an open branched entropy circuit. Themachine uses a fluid in which the compressible component is air. The airis drawn in from the atmosphere at the inlet 7 and mixed with anincompressible fluid (e.g. water) in the mixer 9. The fluid isaccelerated in a convergent nozzle 2 and fed to a turbomachine 1.Downstream of the divergent nozzle 3, the air is separated in theseparator 7 and fed to the compressor 5.2. The compressor 5.2 increasesthe pressure of the air to atmospheric pressure and thus ensures thereis a negative pressure in the mixer 9. The heated air then flows backinto the atmosphere via the outlet 10. The pressure of the cooler,incompressible component of the fluid is increased to atmosphericpressure in the compressor 5.1. At the heat exchanger 8, the thermalenergy Q₁ extracted from the air is returned to the incompressiblefluid.

FIG. 9 shows a heat engine with a branched entropy circuit (see FIG. 9). The heat engine works in the same way as the heat pump in FIG. 7 . Inthe entropy circuit I_(S2), the thermal energy Q₂ is first dissipated inthe heat exchanger 8.2 and then the fluid is compressed in thecompressor 5.2. Due to a low heat capacity of the fluid component in theentropy circuit I_(S2) in relation to I_(S1), only little thermal energyhas to be dissipated.

FIG. 10 shows a hydropower machine for further application of themethod, which converts potential and thermal energy into mechanicalenergy. The water flows from the upper reservoir 11 to the lowerreservoir 12. The turbomachine 1, designed as a turbine, is arrangedbelow the upper reservoir. The entropy flow of the water I_(S1) is mixedwith air I_(S2) and accelerated in a convergent nozzle 2 with a mixer(e.g., a Venturi or jet-stream nozzle). The air being cooled by theacceleration extracts vibrational and rotational energy from the watermolecules and expands almost isothermally. At the same time, the watermolecules are accelerated with the air and release their kinetic energyto the turbine 1. The water is separated from the air in the turbinehousing 1.1. The water collects at the bottom of the turbine housing 1.1and is accelerated with a gravitational divergent nozzle. With a fall of10 m or more, this increases the pressure by about 1 bar, therebycreating a vacuum on the turbine housing 1.1. To maintain this negativepressure, the air must be pumped out through the air duct 14, e.g., bymeans of a piston pump or a jet-stream pump 13.

LIST OF REFERENCES

-   M Molecule-   1 Turbomachine-   1.1 Housing-   2 Convergent nozzle-   3 Divergent nozzle-   4 Rotational axis-   Compressor-   5.1 Compressor-   5.2 Compressor-   6 Balancing vessel-   7 Separator-   8 Heat exchanger-   8.1 Heat exchanger-   8.2 Heat exchanger-   9 Mixer-   10 Outlet-   11 Reservoir-   12 Reservoir-   13 Jet-stream pump-   14 Air duct

1. A method for increasing the efficiency of a turbomachine, wherein afluid guided through the turbomachine transmits kinetic energy to theturbomachine, characterised in that the fluid or at least one fluidcomponent of the fluid is compressible, and in that the flow velocity ofthe fluid, which is reduced in the turbomachine during the transmissionof the kinetic energy, is increased directly downstream of theturbomachine by a force FB, generated by a force field and acting in thedirection of flow, by converting potential energy of the fluid intokinetic energy of the fluid to such an extent that the pressure of thefluid, which is reduced in the turbomachine, is thereby increased againto at least 0.1 times the pressure of the fluid upstream of theturbomachine.
 2. A method for increasing the efficiency of aturbomachine, wherein a fluid guided through the turbomachine transmitskinetic energy to the turbomachine, characterized in that the fluid hastwo fluid components and at least one fluid component of the fluid iscompressible, and in that, in the working temperature range, the ratiocp/cV of the second fluid component is at least 1.1 times the ratiocp/cV of the first fluid component, and in that the fluid components areseparated downstream of the turbomachine in a separator, and in that thefirst fluid component is accelerated and/or compressed downstream of theseparator in a first compressor and the second fluid component isaccelerated in a second compressor downstream of the separator, and inthat, downstream of the first and second compressors, the two fluidcomponents are combined again in a mixer and in that the mass flows ofthe fluid components are dimensioned in such a way that an entropy flowIS1 of the first fluid component at the first compressor is greater thanan entropy flow IS2 of the second fluid component at the secondcompressor and an entropy flow downstream of the mixer at the inlet ofthe turbomachine is the sum of IS1 and IS2.
 3. The method of claim 1,wherein the compressible fluid is accelerated in a nozzle in thedirection of flow upstream of the turbomachine.
 4. The method of claim1, wherein a divergent nozzle and/or a compressor is arranged downstreamof the turbomachine in the direction of flow.
 5. The method of claim 1,wherein the fluid is a multiphase flow and at least one fluid componentis gaseous and another fluid component of the fluid is liquid.
 6. Themethod of claim 1, wherein a fluid mixture consisting of a first fluidand a second fluid is used as the compressible fluid and that the firstfluid has a lower vapour pressure than the second fluid, and that thefirst fluid is liquid both during acceleration at the convergent nozzleand downstream of the turbomachine, and that the second fluid is atleast partially gaseous during acceleration at the convergent nozzle andliquid downstream of the divergent nozzle.
 7. The method of claim 1,wherein a fluid mixture consisting of a first fluid and a second fluidis used as the compressible fluid, wherein the first fluid is a gas andthe second fluid is a liquid, and in that the first fluid is dissolvedin the second fluid before acceleration at the convergent nozzle, isreleased from the second fluid during acceleration at the convergentnozzle and is dissolved again in the second fluid downstream of thedivergent nozzle.
 8. The method of claim 1, wherein the force FB actingin the direction of flow is a gravitational force, a centrifugal force,a magnetic force, an electrical force or a mechanical force provided bya further turbomachine.
 9. The method of claim 1, wherein theturbomachine is a turbine or an MHD generator.
 10. The method of claim2, wherein the compressible fluid is accelerated in a nozzle in thedirection of flow upstream of the turbomachine.
 11. The method of claim2, wherein a divergent nozzle and/or a compressor is arranged downstreamof the turbomachine in the direction of flow.
 12. The method of claim 2,wherein the fluid is a multiphase flow and at least one fluid componentis gaseous and another fluid component of the fluid is liquid.
 13. Themethod of claim 2, wherein a fluid mixture consisting of a first fluidand a second fluid is used as the compressible fluid and that the firstfluid has a lower vapour pressure than the second fluid, and that thefirst fluid is liquid both during acceleration at the convergent nozzleand downstream of the turbomachine, and that the second fluid is atleast partially gaseous during acceleration at the convergent nozzle andliquid downstream of the divergent nozzle.
 14. The method of claim 2,wherein a fluid mixture consisting of a first fluid and a second fluidis used as the compressible fluid, wherein the first fluid is a gas andthe second fluid is a liquid, and in that the first fluid is dissolvedin the second fluid before acceleration at the convergent nozzle, isreleased from the second fluid during acceleration at the convergentnozzle and is dissolved again in the second fluid downstream of thedivergent nozzle.
 15. The method of claim 2, wherein the force FB actingin the direction of flow is a gravitational force, a centrifugal force,a magnetic force, an electrical force or a mechanical force provided bya further turbomachine.
 16. The method of claim 2, wherein theturbomachine is a turbine or an MHD generator.